| Applies To | |||
| Product(s): | AutoPIPE | ||
| Version(s): | ALL | ||
| Environment: | N/A | ||
| Area: | Modeling | ||
| Original Author: | Bentley Technical Support Group | ||
| Date Logged & Current Version | Aug. 2015 09.06.02.06 | ||
Problem:
How to model a Viscous Damper in AutoPIPE?
Solution:
Dampers
Following extract from AutoPIPE online help:
When Damper is entered in the Support type field, the Support dialog is updated to include additional fields. Vibration dampers are active only for static seismic and dynamic load cases (E1 - E3, R1-R10, S1-S3, F1-F3, H1-H3, M1-M3); they have zero stiffness for all other load cases. A damper may act along one of the global axes or in a specified direction. When all of the data is entered, accept the dialog by clicking on OK; the Damper support symbol will then be drawn at the specified point as shown.
Typically for a static earthquake analysis E1 to E3 a damper element is used to lock up (i.e stiffness = rigid only acts in the E1 to E3 cases) the pipe but be 'free" in the thermal case. What you are describing I assume is the viscous component of the damper to overcome in order to move or lock up the damper. This is usually not a consideration for stress analysis of static seismic cases where it is assumed the snubber is designed to 'lock up' under earthquake (because of the nature of the suddenly applied load, the viscous force is so high such as to act as a rigid restraint) then move under a slowly applied load like thermal. There will be some resistance to movement in the thermal case due to the viscous dampening action but in AutoPIPE automatically assumes zero stiffness.
The damper stiffness =RIGID is commonly used.
In the dynamic analysis like time history again the damper is assumed to 'lock up' depending on the stiffness.
Yes it may be appropriate to enter the Ns/m (ie Force/Velocity) for the snubber but AutoPIPE can only handle constant stiffness acting supports across the full travel of the pipe support. And again the dampening action is assumed almost instantaneous such the damper will act as a rigid restraint.
The following Enhancement has been logged:
TFS-E138946 (CAE-CR-10939) - Update damper support to viscous damper